A wave absorber for an anechoic chamber, specifically for an antenna pattern measurement, is required to have higher (e.g., about 30-40 dB) wave absorption performance than ordinary wave absorbers. Japanese Patent Unexamined Publication No. 4-144197/1992 proposes a wave absorber for use in an anechoic chamber, which is produced by preparing a material by adhering foamed organic polymer beads with one another using an adhesive, which particles having a surface layer made from a conductive material such as carbon black and graphite, and forming the material into a desired shape such as a quadratic pyramid, cone, wedge and the like.
Of the formed products proposed therein, particularly that having a quadratic pyramidal shape, which is known to achieve superior wave absorption performance, is associated with a problem that the vertex of the quadratic pyramid is decayed by a short-term use to result in drastic degradation of wave absorption performance.
According to the studies by the present inventors, the adhesion between foamed organic polymer beads in the formed product proposed in the above publication is achieved only by the adhesion of an extremely thin resin binder contained in the conductive layer, and said adhesion has been found to decrease during a short-term use of the wave absorber.
It is therefore an object of the present invention to provide a wave absorber superior in a long-term shape retention, which is made of foamed organic polymer particles having a conductive layer on the surface thereof, and a method of production thereof.